The present invention relates to shampoo compositions, and more particularly to shampoo compositions containing sunscreen materials to protect the hair from the harmful effects of sunlight.
Dark hair exposed to sunlight fades, oriental black hair takes on a reddish tinge, and blond hair tends to yellow. The hair becomes rougher and drier to the touch after prolonged exposure to sunlight and also tends to lose its glossy appearance.
The hair can be protected from damage by exposure to sunlight by coating the hair fibres with an effective sunscreen.
It is reported, for example, in U.S. Pat. No. 4 488 564 (L'Oreal) that ultra-violet (UV) filters can be added to shampoo compositions to combat the adverse effects of sunlight on the composition itself. Such compositions tend to fade and to destabilise if left exposed to sunlight for long periods of time. The UV filters used are generally water-soluble, and present in very small amounts.
EP 117 135 (Johnson and Johnson) discloses the use of a water-soluble non-particulate sunscreen, especially para-amino benzoic acid, in a shampoo composition which contains an anionic nitrogen-containing polymer.
We have found however, that sunscreens which are water-soluble do not confer a significant degree of protection on the hair when used in shampoo compositions. These sunscreens are easily removed from the hair in the final rinse step of the washing procedure.
Detergent compositions, for example shampoos, comprising an anionic surfactant, water-insoluble particles and a cationic polymer have been described in U.S. Pat. No. 3 580 853 (Parran). In the detergent compositions described in that patent the cationic polymers are water-soluble cationic nitrogen containing polymers having a molecular weight within the range from 2,000 to 3,000,000 and have a cationic charge density greater than 0.001 in aqueous solution. The "cationic charge density" of a polymer as that term is used in the U.S. patent, refers to the ratio of the number of positive charges on a monomeric unit of which the polymer is comprised to the molecular weight of the monomeric unit. The cationic charge density multiplied by the polymer molecular weight determines the number of positively charged active sites of a given polymer chain. The Parran patent states that the cationic polymer can be employed in the detergent composition at a concentration within the range from about 0.1% to about 10% by weight, preferably from about 0.25% to about 4.0% by weight.
We have investigated the mode of action of the enhancement of deposition of particulate materials from liquid detergent compositions of the Examples of the Parran patent containing an anionic surfactant and it appears that the enhancement derives from the presence in the washing composition of a complex between the anionic surfactant and the cationic polymer which is formed upon dilution of the detergent composition. The formation of complexes between cationic polymers and anionic surfactants is well-known and is described in Norda Briefs, No. 464, Feb., 1975. This article mentions that such complexes may be solubilised at increased surfactant levels and also refers to the deposition of the water-insoluble complex onto the hair during the shampooing process. The Norda Briefs article refers in particular to those complexes formed using the quarternary nitrogen-substituted cellulose ether derivatives (available commerically under the trade name Polymer JR) which the Parran patent states as particularly efficacious for enhancing the deposition of particulate substances.
Our experiments have indicated that in the Parran formulations comprising an anionic surfactant, complexes between the cationic polymer and anionic surfactant precipitate or separate upon dilution during use and that it is essential for this to occur if an enhancement in the deposition of the particulate substance is to be obtained from the Parran compositions containing an anionic surfactant. While precipitation of the complex and its deposition onto the hair may give a benefit in its own right, for such deposition leads to improved hair condition, more particularly improved ease of combing, such deposition of substantial amounts of cationic polymer is not always desired by the user.
Washing compositions comprising an anionic surfactant, a water-insoluble particulate substance and a water-soluble cationic polymer are described in EP 93 601 (Unilever, Sime). The compositions described contain non-cellulose cationic polymer having a cationic charge density (as defined above) of from 0.0001 to 0.0017 and a molecular weight of from 2,000 to 3,000,000.
The particulate substance may comprise oily materials which are pre-emulsified in a solution of anionic surfactant and stabilised using emulsifier to give oil "particles" having an average particle diameter of from 0.2 to 50 .mu.m.
It is believed that the cationic polymer forms a coating on the surface of the water-insoluble particles which coating has loops which extend into the detergent system, providing positively charged bridges for attachment to negative sites on the substrate. It is essential in the Sime patent that formation of a water-insoluble complex between the cationic polymer and anionic surfactant is avoided, and this is achieved by using low concentrations of polymer having a low cationic charge density, and high concentrations of anionic surfactant. Use of higher concentrations of cationic polymer is said to give precipitation of a cationic/anionic complex which is undersirable for deposition of the particles.
We have found that deposition of water-insoluble normally-liquid sunscreens which have not been pre-emulsified can be achieved at concentrations of cationic polymer which also show conditioning benefit. These liquid sunscreens can be added to shampoos to give a clear solution, in which the sunscreen is solubilised in the micelle of the surfactant, and is not present in particulate or droplet form. It was therefore not expected to obtain enhanced deposition using the Parran or Sime technology. However, the Applicant has found a class of polymer (quaternised polygalactomannan gums) which enhances deposition. The precise mechanism is uncertain, but differs from that of Parran or Sime as no particle or phase separation is necessary for the effect to be seen.